8.25.16 Lecture Flashcards
Biological membranes are primarily composed of ___ and ___; what is the ratio of these two components?
Lipids; proteins; on average, 50:50, although proteins can range from 25%-75%
Why are biological membranes important?
Membranes function as efficient barriers for diffusion, preventing the mixing of distinct environments, allowing for compartmentalization, and ultimately making life possible.
What is the most abundant membrane lipid?
Phospholipid
Describe the general structure of phospholipid.
1 polar head (exposed charge), 2 long fatty acid tails attached to a 3 carbon backbone (often carbon or sphingosine)
What dictates membrane fluidity?
Length and saturation of fatty acids
What is cholesterol?
A lipid molecule present in large amounts in plasma membranes; has a polar head group, rigid steroid ring structure, and nonpolar hydrocarbon tail
Increasing membrane rigidity has what effect on the permeability of the bilayer to water soluble molecules?
Decreases permeability
Hydrophobic molecules self-aggregate in water. Why?
Self-aggregation is energetically favorable because it is less costly than organizing water molecules around the hydrophobic surfaces of individual lipids.
What dictates the shape of the micelle?
The shape of the lipid
What explains the ability of a membrane to spontaneously reseal when torn?
Self-aggregation
Self-aggregation also provides tremendous ___ to membranes, helping to prevent rupture under stress.
Plasticity
What type of movement is common in lipids in membranes?
Lateral diffusion
Fluidity of a membranes depends on what two factors?
Lipid composition and temperature
What is membrane fluidity?
The relative mobility of lipids within a membrane
What is transition temperature?
The temperature at which homogenous lipid bilayer transitions from a liquid state to a more solid gel state (“freezing”)
More fluid membranes have a ___ transition temperature.
Lower
How is transition temperature lowered and fluidity increased?
Increase double bonds (introduces kinks), decrease length of hydrocarbon tails.
What is the difference between saturated and unsaturated chains?
Unsaturated chains have cis double bonds; saturated chains do not.
What are lipid rafts?
A type of microdomain; Cholesterol and sphingolipid rich regions of transient self-associations caused by van der Waals forces and associated with cell signaling.
Where are glycolipids always found?
On the monolayer facing away from the cytosol
Where are negatively charged phospholipids found?
On the cytosolic side
What are needed to move phospholipids between monolayer?
Translocases and flipases
What are glycolipids?
Glycosylated phopholipids
Glycolipids exhibit extreme ___.
Asymmetry
Where are glycolipids generated?
The lumen of the Golgi
How is apoptosis triggered?
Phosphotidylserine translocates to the exterior membrane in apoptotic cells by scramblase and lack of activity of PS-translocases
Lipid bilayer constituents drive ___ through what two general methods?
Signal transduction; acting as a scaffold or as a second messenger
Bilayers have both hydrophobic and hydrophilic regions. Transmembranes proteins have similar properties. Where do the various amino acids localize?
Hydrophobic amino acids interact with the core of the bilayer and are buried in the membrane. Hydrophilic amino acids are located on the inner and outer membranes, though polar amino acids can be found in the membranes.
What are the general types of proteins?
- Transmembrane proteins (typically alpha helices)
- Transmembrane proteins that span multiple times
- Transmembrane proteins (beta barrels)
- Amphipathic proteins
- Proteins modified with a moiety
- GPI-linked proteins
What provides a hydrophobic anchor that keeps proteins associated with bilayers without inserting into the bilayer itself? What are the three kinds of anchors?
Fatty acid modifications of proteins; myrisotyl, palmitoyl, farnesyl
What can help determine the presence of a transmembrane protein?
Hydropathy plots
___% of proteins are likely membrane proteins.
30
What form large pores in the lipid bilayer?
Beta barrels
Many membrane proteins diffuse ___ along the bilayer plane. Others are anchored via ___ proteins.
Laterally; cytoskeleton
Cell-to-cell communication occurs via a combination of…
…membrane biophysics and cytoskeletal organization, which create dynamic membrane behavior critical for many cellular activities.
